Descartes’s answer to skepticism

Notes for October 8

Main points

The First Meditation left us with skepticism about our knowledge of the external world, meaning the world outside our minds. Descartes set a standard for knowledge that, he argued, beliefs based on the senses cannot meet. Since we rely on the senses for knowledge of the external world, it follows that we know nothing about the external world. Bummer.

The Second and Third Meditations try to show how we can use reason, an intellectual process distinct from the sensory ones, to supply a foundation for our beliefs based on the senses. Specifically, Descartes maintained, I can use reason to establish with certainty that I exist, that extension is the essential property of bodies, that God exists, and that we are not fundamentally deceived about our reasoning. This last point comes from an assumption: that God, as a perfect being, would not allow us to be deceived. So knowledge based on the senses rests on a foundation established by reason, namely, the certainty that God exists and that God would not allow us to be deceived.

We spent most of our time talking about two points in the Second Meditation: Descartes’s famous “I think, therefore I am” or cogito argument (in latin, it’s “cogito ergo sum”) and his geometrical conception of physical bodies (remember the wax).

God and knowledge

The Third meditation gives two arguments for God’s existence. The point of these was to establish that God is perfect and therefore would not allow us to be deceived in our basic reasoning: compare p. 35 (AT 52) with p. 25 (AT 36).AT xx means the numbers in the margin. They’re pages in the standard edition of Descartes’s works, edited by Adam and Tannery.

We ran a bit short on time at the end. I passed out a handout of two famous criticisms of Descartes and I wanted to take this opportunity to explain them at greater length.

Arnauld’s objection claims that Descartes’s argument is caught in a circle: in order to establish certainty about our reasoning, he needs to establish that God exists, but in order to establish that God exists, he needs to establish certainty about our reasoning. This is known as the Cartesian Circle.

Descartes might be able to break out of the Cartesian Circle if he can establish certainty about our reasoning that is immune from manipulation even by a supernatural being. As we saw, he was inclined to say something like that. But he was also of two minds about it, and concluded that he really had to show that God exists and would not deceive us in order to have full confidence in his reasoning about anything.

The other objection we discussed comes from Bayle. He noted that Descartes himself claimed that God allows us to be mistaken about the external world. We think that objects like the wax have colors and smells but, according to Descartes, that’s an illusion. Colors, smells, and other sensory properties are added by us. In fact, objects only have extension. But if God is willing to let us be that far deceived, why not allow us to be deceived about the existence of the external world altogether?

Finally, take a look at the last paragraph from the Third Meditation. There, Descartes talks about how we’re made in the image of God. I don’t think that’s rhetorical puffery; I think it reflects how Descartes thought of us. Hume, by contrast, thought the idea was a fundamentally mistaken. Or so I’ll argue.

Augustine and Descartes

Did you know that Descartes was not the first to employ the cogito argument (“I think, therefore I am”)? St. Augustine got there first.

And we indeed recognize in ourselves the image of God, that is, of the supreme Trinity, an image which, though it be not equal to God, or rather, though it be very far removed from Him,—being neither co-eternal, nor, to say all in a word, consubstantial with Him,—is yet nearer to Him in nature than any other of His works, and is destined to be yet restored, that it may bear a still closer resemblance.  For we both are, and know that we are, and delight in our being, and our knowledge of it.  Moreover, in these three things no true-seeming illusion disturbs us; for we do not come into contact with these by some bodily sense, as we perceive the things outside of us,—colors, e.g., by seeing, sounds by hearing, smells by smelling, tastes by tasting, hard and soft objects by touching,—of all which sensible objects it is the images resembling them, but not themselves which we perceive in the mind and hold in the memory, and which excite us to desire the objects.  But, without any delusive representation of images or phantasms, I am most certain that I am, and that I know and delight in this.

In respect of these truths, I am not at all afraid of the arguments of the Academicians, who say, What if you are deceived?  For if I am deceived, I am. For he who is not, cannot be deceived; and if I am deceived, by this same token I am.  And since I am if I am deceived, how am I deceived in believing that I am? for it is certain that I am if I am deceived.  Since, therefore, I, the person deceived, should be, even if I were deceived, certainly I am not deceived in this knowledge that I am.  And, consequently, neither am I deceived in knowing that I know. For, as I know that I am, so I know this also, that I know.  And when I love these two things, I add to them a certain third thing, namely, my love, which is of equal moment.  For neither am I deceived in this, that I love, since in those things which I love I am not deceived; though even if these were false, it would still be true that I loved false things.  For how could I justly be blamed and prohibited from loving false things, if it were false that I loved them?  But, since they are true and real, who doubts that when they are loved, the love of them is itself true and real?  Further, as there is no one who does not wish to be happy, so there is no one who does not wish to be.  For how can he be happy, if he is nothing?Saint Augustine, The City of God Against the Pagans, (composed between 413 and 426 AD), Book XI, Ch.26.

Key concepts

  1. Why Descartes thinks it’s impossible to doubt his own existence and what this shows.
  2. The example of the wax and Descartes’s geometrical conception of the physical world.
This page was written by Michael Green for Problems of Philosophy, Philosophy 1, Fall 2013. It was posted October 8, 2013.
Problems of Philosophy